Temperature regulation of an inductor assembly

ABSTRACT

A vehicle is provided with a transmission having an inductor assembly. The inductor assembly is mounted within the transmission such that it is directly cooled by transmission fluid through at least one of spraying, splashing and immersion. The transmission includes at least one gear that is configured to, when rotating, transmit torque between an input and output of the transmission and splash fluid onto the inductor assembly to cool the inductor assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/673,731,filed Nov. 9, 2012, now U.S. Pat. No. ______ the disclosure of which ishereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

One or more embodiments relate to an inductor assembly of a DC-DCconverter that is mounted inside of a transmission housing.

BACKGROUND

The term “electric vehicle” as used herein, includes vehicles having anelectric machine for vehicle propulsion, such as battery electricvehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybridelectric vehicles (PHEV). A BEV includes an electric machine, whereinthe energy source for the electric machine is a battery that isre-chargeable from an external electric grid. In a BEV, the battery isthe source of energy for vehicle propulsion. A HEV includes an internalcombustion engine and one or more electric machines, wherein the energysource for the engine is fuel and the energy source for the electricmachine is a battery. In a HEV, the engine is the main source of energyfor vehicle propulsion with the battery providing supplemental energyfor vehicle propulsion (the battery buffers fuel energy and recoverskinematic energy in electric form). A PHEV is like a HEV, but the PHEVhas a larger capacity battery that is rechargeable from the externalelectric grid. In a PHEV, the battery is the main source of energy forvehicle propulsion until the battery depletes to a low energy level, atwhich time the PHEV operates like a HEV for vehicle propulsion.

Electric vehicles may include a voltage converter (DC-DC converter)connected between the battery and the electric machine. Electricvehicles that have AC electric machines also include an inverterconnected between the DC-DC converter and each electric machine. Avoltage converter increases (“boosts”) or decreases (“bucks”) thevoltage potential to facilitate torque capability optimization. TheDC-DC converter includes an inductor (or reactor) assembly, switches anddiodes. A typical inductor assembly includes a conductive coil that iswound around a magnetic core. The inductor assembly generates heat ascurrent flows through the coil. An existing method for cooling the DC-DCconverter by circulating fluid through a conduit that is proximate tothe inductor is disclosed in U.S. 2004/0045749 to Jaura et al.

SUMMARY

In one embodiment, a vehicle is provided with a transmission having aninductor assembly and at least one gear that is configured to, whenrotating, transmit torque between an input and output of thetransmission and splash fluid onto the inductor assembly to cool theinductor assembly.

In another embodiment, a transmission is provided with a housing and acylindrical inductor assembly that is disposed within the housing. Thecylindrical inductor assembly includes a coil having exposed exteriorsurface area portions and a core formed onto the coil such that at leasta portion of the exterior surface area portions is exposed to fluidwithin the transmission to cool the coil.

In yet another embodiment, a transmission is provided with a housing anda planar inductor assembly. The planar inductor assembly includes aninsulative bobbin, a coil wound around the bobbin and having exposedsurface area portions, and a core supported by the bobbin. The planarinductor assembly is disposed within the housing such that at least aportion of the exposed surface area portions is exposed to fluid withinthe housing to cool the coil.

In still yet another embodiment, a transmission is provided with ahousing and an inductor assembly disposed within the housing. Thetransmission also includes at least one element that is adapted to, whenrotating, transmit torque between an input and output of thetransmission and displace cooling fluid onto the inductor assembly.

As such, the inductor assembly provides advantages over existinginductor assemblies by facilitating direct cooling of the conductor andcore using transmission fluid. The inductor assembly is mounted withinthe transmission chamber such that it is directly cooled by transmissionfluid through spraying, splashing and/or immersion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a transmission and a variable voltageconverter (VVC) having an inductor assembly, and illustrating threedifferent regions for mounting the inductor assembly within thetransmission according to one or more embodiments;

FIG. 2 is a schematic diagram of a vehicle including the transmissionand the VVC of FIG. 1;

FIG. 3 is a circuit diagram of the VVC of FIG. 1;

FIG. 4 is a section view of an inductor assembly according to anotherembodiment;

FIG. 5 is an enlarged front perspective view of the inductor assembly ofFIG. 1;

FIG. 6 is an enlarged side perspective view of a portion of FIG. 1illustrating the inductor assembly mounted in an upper region;

FIG. 7 is a diagram illustrating a thermal resistance network forcooling the inductor assembly of FIG. 5;

FIG. 8 is a graph illustrating a comparison of the steady-state thermalresistance of the inductor assemblies of FIG. 4 and FIG. 5;

FIG. 9 is a graph illustrating a comparison of the thermal impedance ofthe inductor assemblies of FIG. 4 and FIG. 5;

FIG. 10 is another front view of the transmission illustrating theinductor assembly of FIG. 1 mounted within an intermediate region,according to one or more embodiments;

FIG. 11 is yet another front view of the transmission illustrating theinductor assembly of FIG. 1 mounted within a lower region, according toone or more embodiments;

FIG. 12 is a rear view of the transmission illustrating the inductorassembly of FIG. 1 mounted within an upper region, according to one ormore embodiments;

FIG. 13 is a front perspective view of an inductor assembly according toanother embodiment; and

FIG. 14 is a front perspective view of an inductor assembly according toyet another embodiment.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

With reference to FIG. 1, a DC-DC converter is illustrated in accordancewith one or more embodiments and is generally referenced by numeral 10.The DC-DC converter 10 may also be referred to as a variable voltageconverter (VVC) 10. The VVC 10 is an assembly with components that aremounted both inside and outside of a transmission 12. The VVC 10includes an inductor assembly 14 that is mounted inside of thetransmission 12 and a number of switches and diodes (shown in FIG. 3)that are mounted outside of the transmission 12. By mounting theinductor assembly 14 within the transmission 12, the inductor assembly14 may be directly cooled by transmission fluid which allows forimproved thermal performance.

Referring to FIG. 2, the transmission 12 is depicted within a plug-inhybrid electric vehicle (PHEV) 16, which is an electric vehiclepropelled by an electric machine 18 with assistance from an internalcombustion engine 20 and connectable to an external power grid. Theelectric machine 18 is an AC electric motor according to one or moreembodiments, and depicted as the “motor” 18 in FIG. 1. The electricmachine 18 receives electrical power and provides drive torque forvehicle propulsion. The electric machine 18 also functions as agenerator for converting mechanical power into electrical power throughregenerative braking.

The transmission 12 has a power-split configuration, according to one ormore embodiments. The transmission 12 includes the first electricmachine 18 and a second electric machine 24. The second electric machine24 is an AC electric motor according to one or more embodiments, anddepicted as the “generator” 24 in FIG. 1. Like the first electricmachine 18, the second electric machine 24 receives electrical power andprovides output torque. The second electric machine 24 also functions asa generator for converting mechanical power into electrical power andoptimizing power flow through the transmission 12.

The transmission 12 includes a planetary gear unit 26, which includes asun gear 28, a planet carrier 30 and a ring gear 32. The sun gear 28 isconnected to an output shaft of the second electric machine 24 forreceiving generator torque. The planet carrier 30 is connected to anoutput shaft of the engine 20 for receiving engine torque. The planetarygear unit 26 combines the generator torque and the engine torque andprovides a combined output torque about the ring gear 32. The planetarygear unit 26 functions as a continuously variable transmission, withoutany fixed or “step” ratios.

The transmission 12 also includes a one-way clutch (O.W.C.) and agenerator brake 33, according to one or more embodiments. The O.W.C. iscoupled to the output shaft of the engine 20 to only allow the outputshaft to rotate in one direction. The O.W.C. prevents the transmission12 from back-driving the engine 20. The generator brake 33 is coupled tothe output shaft of the second electric machine 24. The generator brake33 may be activated to “brake” or prevent rotation of the output shaftof the second electric machine 24 and of the sun gear 28. In otherembodiments, the O.W.C. and the generator brake 33 are eliminated, andreplaced by control strategies for the engine 20 and the second electricmachine 24.

The transmission 12 includes a countershaft having intermediate gearsincluding a first gear 34, a second gear 36 and a third gear 38. Aplanetary output gear 40 is connected to the ring gear 32. The planetaryoutput gear 40 meshes with the first gear 34 for transferring torquebetween the planetary gear unit 26 and the countershaft. An output gear42 is connected to an output shaft of the first electric machine 18. Theoutput gear 42 meshes with the second gear 36 for transferring torquebetween the first electric machine 18 and the countershaft. Atransmission output gear 44 is connected to a driveshaft 46. Thedriveshaft 46 is coupled to a pair of driven wheels 48 through adifferential 50. The transmission output gear 44 meshes with the thirdgear 38 for transferring torque between the transmission 12 and thedriven wheels 48.

The vehicle 16 includes an energy storage device, such as a battery 52for storing electrical energy. The battery 52 is a high voltage batterythat is capable of outputting electrical power to operate the firstelectric machine 18 and the second electric machine 24. The battery 52also receives electrical power from the first electric machine 18 andthe second electric machine 24 when they are operating as generators.The battery 52 is a battery pack made up of several battery modules (notshown), where each battery module contains a plurality of battery cells(not shown). Other embodiments of the vehicle 16 contemplate differenttypes of energy storage devices, such as capacitors and fuel cells (notshown) that supplement or replace the battery 52. A high voltage buselectrically connects the battery 52 to the first electric machine 18and to the second electric machine 24.

The vehicle includes a battery energy control module (BECM) 54 forcontrolling the battery 52. The BECM 54 receives input that isindicative of vehicle conditions and battery conditions, such as batterytemperature, voltage and current. The BECM 54 calculates and estimatesbattery parameters, such as battery state of charge and the batterypower capability. The BECM 54 provides output (BSOC, P_(cap)) that isindicative of the BSOC and the battery power capability to other vehiclesystems and controllers.

The transmission 12 includes the VVC 10 and an inverter 56. The VVC 10and the inverter 56 are electrically connected between the main battery52 and the first electric machine 18; and between the battery 52 and thesecond electric machine 24. The VVC 10 “boosts” or increases the voltagepotential of the electrical power provided by the battery 52. The VVC 10also “bucks” or decreases the voltage potential of the electrical powerprovided by the battery 52, according to one or more embodiments. Theinverter 56 inverts the DC power supplied by the main battery 52(through the VVC 10) to AC power for operating the electric machines 18,24. The inverter 56 also rectifies AC power provided by the electricmachines 18, 24, to DC for charging the main battery 52. Otherembodiments of the transmission 12 include multiple inverters (notshown), such as one invertor associated with each electric machine 18,24.

The transmission 12 includes a transmission control module (TCM) 58 forcontrolling the electric machines 18, 24, the VVC 10 and the inverter56. The TCM 58 is configured to monitor, among other things, theposition, speed, and power consumption of the electric machines 18, 24.The TCM 58 also monitors electrical parameters (e.g., voltage andcurrent) at various locations within the VVC 10 and the inverter 56. TheTCM 58 provides output signals corresponding to this information toother vehicle systems.

The vehicle 16 includes a vehicle system controller (VSC) 60 thatcommunicates with other vehicle systems and controllers for coordinatingtheir function. Although it is shown as a single controller, the VSC 60may include multiple controllers that may be used to control multiplevehicle systems according to an overall vehicle control logic, orsoftware.

The vehicle controllers, including the VSC 60 and the TCM 58 generallyincludes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH,ROM, RAM, EPROM and/or EEPROM) and software code to co-act with oneanother to perform a series of operations. The controllers also includepredetermined data, or “look up tables” that are based on calculationsand test data and stored within the memory. The VSC 60 communicates withother vehicle systems and controllers (e.g., the BECM 54 and the TCM 58)over one or more wired or wireless vehicle connections using common busprotocols (e.g., CAN and LIN). The VSC 60 receives input (PRND) thatrepresents a current position of the transmission 12 (e.g., park,reverse, neutral or drive). The VSC 60 also receives input (APP) thatrepresents an accelerator pedal position. The VSC 60 provides outputthat represents a desired wheel torque, desired engine speed, andgenerator brake command to the TCM 58; and contactor control to the BECM54.

The vehicle 16 includes a braking system (not shown) which includes abrake pedal, a booster, a master cylinder, as well as mechanicalconnections to the driven wheels 48, to effect friction braking. Thebraking system also includes position sensors, pressure sensors, or somecombination thereof for providing information such as brake pedalposition (BPP) that corresponds to a driver request for brake torque.The braking system also includes a brake system control module (BSCM) 62that communicates with the VSC 60 to coordinate regenerative braking andfriction braking. The BSCM 62 provides a regenerative braking command tothe VSC 60, according to one embodiment.

The vehicle 16 includes an engine control module (ECM) 64 forcontrolling the engine 20. The VSC 60 provides output (desired enginetorque) to the ECM 64 that is based on a number of input signalsincluding APP, and corresponds to a driver's request for vehiclepropulsion.

The vehicle 16 is configured as a plug-in hybrid electric vehicle (PHEV)according to one or more embodiments. The battery 52 periodicallyreceives AC energy from an external power supply or grid, via a chargeport 66. The vehicle 16 also includes an on-board charger 68, whichreceives the AC energy from the charge port 66. The charger 68 is anAC/DC converter which converts the received AC energy into DC energysuitable for charging the battery 52. In turn, the charger 68 suppliesthe DC energy to the battery 52 during recharging.

Although illustrated and described in the context of a PHEV 16, it isunderstood that embodiments of the VVC 10 may be implemented on othertypes of electric vehicles, such as a HEV or a BEV.

With reference to FIG. 3, the VVC 10 includes a first switching unit 78and a second switching unit 80 for boosting the input voltage (V_(bat))to provide output voltage (V_(dc)). The first switching unit 78 includesa first transistor 82 connected in parallel to a first diode 84, butwith their polarities switched (anti-parallel). The second switchingunit 80 includes a second transistor 86 connected anti-parallel to asecond diode 88. Each transistor 82, 86 may be any type of controllableswitch (e.g., an insulated gate bipolar transistor (IGBT) orfield-effect transistor (FET)). Additionally, each transistor 82, 86 isindividually controlled by the TCM 58. The inductor assembly 14 isdepicted as an input inductor that is connected in series between themain battery 52 and the switching units 78, 80. The inductor 14generates magnetic flux when a current is supplied. When the currentflowing through the inductor 14 changes, a time-varying magnetic fieldis created, and a voltage is induced. Other embodiments of the VVC 10include different circuit configurations (e.g., more than two switches).

Referring back to FIG. 1, the transmission 12 includes a transmissionhousing 90, which is illustrated without a cover to show internalcomponents. As described above, the engine 20, the motor 18 and thegenerator 24 include output gears that mesh with corresponding gears ofthe planetary gear unit 26. These mechanical connections occur within aninternal chamber 92 of the transmission housing 90. A power electronicshousing 94 is mounted to an external surface of the transmission 12. Theinverter 56 and the TCM 58 are mounted within the power electronicshousing 94. The VVC 10 includes components (e.g., the switches 78, 80and diodes 84, 88 shown in FIG. 3) that are mounted within the powerelectronics housing 94 and the inductor assembly 14 which is mountedwithin the chamber 92 of the transmission housing 90.

The transmission 12 includes fluid 96 such as oil, for lubricating andcooling the gears located within the transmission chamber 92 (e.g., theintermediate gears 34, 36, 38). The transmission chamber 92 is sealed toretain the fluid 96. The transmission 12 also includes pumps andconduits (not shown) for circulating the fluid 96 through the chamber92.

Rotating elements (e.g., intermediate gear 36 and shaft 39, shown inFIG. 6) may displace or “splash” fluid 96 on other components. Such a“splash” region is referenced by letter “A” in FIG. 1 and is located inan upper portion of the chamber 92. In region A, the inductor assembly14 is cooled by transmission fluid 96 that splashes off of the rotatingelements (e.g., the second intermediate gear 36, the shaft 39 (shown inFIG. 6) and the differential 50) as they rotate.

The transmission 12 includes nozzles 98 for directly spraying thetransmission fluid 96 on components within the housing 90, according toone or more embodiments. Such a “spray” region is referenced by letter“B” in FIG. 1 and is located in an intermediate portion of the chamber92. The inductor assembly 14 may be mounted within region B (as shown inFIG. 10) and cooled by transmission fluid 96 that sprays from the nozzle98. The inductor assembly 14 may also receive transmission fluid 96 thatsplashes off of proximate rotating elements (e.g., the planetary gearunit 26). Other embodiments of the transmission 12 contemplate multiplenozzles (nozzles) one or more nozzles that are mounted in otherlocations of the chamber 92 (e.g., a nozzle mounted in region A).

Further, the transmission fluid 96 accumulates within a lower portion ofthe chamber 92. Such an “immersion” region is referenced by letter “C”in FIG. 1 and is located in a lower portion of the chamber 92. Theinductor assembly 14 may be mounted within region C (as shown in FIG.11) and immersed in the transmission fluid 96.

FIG. 4 illustrates an inductor assembly 100 that is configured forindirect cooling according to an existing method. Such an inductorassembly 100 is mounted external of the transmission housing 90 (e.g.,within the power electronics housing 94 of FIG. 1). The inductorassembly 100 includes a conductor 110 that is wrapped around a magneticcore 112. The magnetic core 112 includes a plurality of core elementsthat are spaced apart to define air gaps 114. Ceramic spacers may beplaced between the core elements to maintain the air gaps 114. Theinductor assembly 100 is encased inside an inductor housing 116 (e.g.,an Aluminum housing) and empty space around the inductor assembly 100 isfilled with a thermally conductive, electrically insulating adhesivematerial, such as a potting compound 118. The inductor housing 116 isclamped to a cold plate 120 and thermal grease 122 is applied betweenthe inductor housing 116 and the cold plate 120. A passage 124 is formedthrough the cold plate 120. Cold fluid or coolant (e.g., 50% water and50% ethylene glycol) flows through the passage 124. Heat transfers byconduction from the conductor 110 and the core 112 to the pottingcompound 118 and then to housing 116, thermal grease 122 and finallyinto the cold plate 120. Heat from the cold plate 120 transfers into thecoolant flowing through the passage 124 by convection. Additionally thecold plate 120 may include fins 126 for transferring heat intosurrounding air by convection.

The thermal resistance of the heat transfer path from the conductor 110to the coolant flowing through the passage 124 of the cold plate 120 ishigh. The thermal grease 122, the potting compound 118 and the coldplate 120 contribute significantly to this resistance. As a result, thethermal performance of this potted inductor assembly 100 is limited andthe temperature of the inductor assembly 100 at various locationsincreases and may exceed predetermined temperature limits at highelectrical power loads. In one or more embodiments, a controller (e.g.,the TCM of FIG. 1) may limit the performance of the inductor assembly100 if temperatures of the inductor assembly 100 exceed suchpredetermined limits.

The temperature of the inductor assembly 100 depends on the amount ofcurrent flowing through the conductor 110 and the voltage potentialacross the conductor 110. Recent trends in electric vehicles includehigher current capability of the inductor. For example, increasedbattery power for the extended electric range in PHEVs and reducedbattery cells for the same power in HEVs result in increased inductorcurrent rating in electric vehicles. Additionally, reduced batteryvoltage also leads to an increase in the inductor ac losses due to ahigher magnitude of high frequency ripple current. Therefore, due toadditional heat generation, the temperature of the inductor assembly 100will generally increase and if heat is not dissipated, the inductortemperature may exceed predetermined limits. One solution is to increasethe cross-sectional area of the conductor coil to reduce inductor lossand also improve heat dissipation (due to more surface area). However,such changes will increase the overall size of the inductor assembly. Alarger inductor assembly may be difficult to package in all vehicleapplications, and larger components affect vehicle fuel economy andcost.

Rather than increase the size of the inductor assembly 100, to improvethe inductor thermal performance and thermal capacity, the inductorassembly 100 may be mounted within the transmission chamber 92 anddirectly cooled using transmission fluid 96 as described with referenceto FIG. 1. The transmission fluid 96 is an electrical insulator whichcan be used in direct contact with electrical components (e.g., theconductor 110 and the core 112). However, excess components associatedwith the inductor assembly 100 may be removed if the assembly 100 issubjected to such direct cooling. For example, the potting compound 118and the aluminum housing 116 may be removed. However, the pottingcompound 118 and the housing 116 support the conductor 110 and the core112. Additionally, vibration is more severe inside of the transmission12, than outside. Therefore the overall structure of the inductorassembly 100 is revised in order to remove the potting compound 118 andhousing 116 and mount the assembly inside of the transmission 12.

FIG. 5 illustrates an inductor assembly 14 that is configured to bemounted within the transmission 12, according to one or moreembodiments. The inductor assembly 14 provides a simplified version ofthe inductor assembly 100 described with reference to FIG. 4, in thatthe excess components (e.g., the potting compound, the aluminum housing,the cold plate and the thermal grease) have been removed. The inductorassembly 14 includes a conductor 210 that is formed into two adjacenttubular coils, a core 212 and an insulator 214. The core 212 has agenerally planar shape with a dual “C” configuration, according to theillustrated embodiment. The insulator 214 physically separates theconductor 210 from the core 212 and is formed of an electricallyinsulating polymeric material, such as Polyphenylene sulfide (PPS).

The conductor 210 is formed of a conductive material, such as copper oraluminum, and wound into two adjacent helical coils. The coils areformed using a rectangular (or flat) type conductive wire by an edgewiseprocess, according to one or more embodiments. An input and output leadextend from the conductor 210 and connect to components that are mountedexternal to the transmission 12 (e.g., the battery 52 and the switches78, 80 as shown in FIGS. 2 and 3). The core 212 is formed of a magneticmaterial, such as an iron silicon alloy powder. The core 212 may beformed as a unitary (one-piece) structure (as shown in FIG. 13), or as aplurality of segments (not shown) to form air gaps within each coil. Theinsulator 214 may be formed as a bobbin structure, where the conductor210 is wound about the bobbin. The insulator 214 includes flanges 216having apertures for receiving fasteners (not shown) for mounting theinductor assembly 14, according to one or more embodiments. Otherembodiments of the inductor assembly 14 contemplate an insulator that isseparate from the bracket, which may be formed of a polymer, paper(e.g., Nomex® Paper), or a coating applied to the conductor (not shown).

Referring to FIG. 6, the inductor assembly 14 may be mounted within thetransmission chamber 94. The inductor assembly 14 is mounted within anupper portion of the transmission chamber 92 in the illustratedembodiment, such that it is directly cooled by the transmission fluid 96that splashes off of gears (e.g., the second intermediate gear 36 andthe differential 50). The inductor assembly 14 generates heat as currentflows through the conductor 210. Heat transfers by convection from theconductor 210 and core 212 to the fluid 96, as the fluid 96 flows overthe inductor assembly 14.

FIG. 7 illustrates a thermal resistance network 300 and a direction ofheat flow for the inductor assembly 14 shown in FIG. 6. A direction ofheat transfer (or heat flow) is represented by arrows and numeral 310.The transmission fluid 312 enters the transmission chamber 314 at aninlet temperature that is represented by variable (T_(oil) _(_) _(in)).Transmission elements that dissipate heat due to power losses arerepresented by resistors in FIG. 7, including the motor resistance 316,the generator resistance 318, the transmission housing resistance 320,and the inductor assembly resistance 322. The fluid 312 is displacedover these elements, and heat transfers into the fluid 312.

In case of the inductor, the heat is generated in the conductor and core(shown in FIG. 6). Since the conductor and core of the inductor assembly14 are directly exposed to the fluid, rather than being coated in apotting compound as shown in the inductor assembly 100 of FIG. 4, heatis effectively dissipated from the inductor assembly 14 without anythermal barrier. The heat loads 316-322 heat the fluid 312 and as aresult, the fluid 312 leaves the transmission chamber 314 at a highertemperature (T_(oil) _(_) _(out)>>T_(oil) _(_) _(in)).

For mathematical simplicity, the bulk average temperature of the inletand outlet fluid 312 may be used to analyze the thermal performance.Therefore the thermal resistance (θ_(inductor)) for splash coolingperformance of the inductor is calculated according to equations 1 and 2as shown below:

$\begin{matrix}{T_{{oil}\_ {avg}} = \frac{T_{{oil}\_ {in}} + T_{{oil}\_ {out}}}{2}} & (1) \\{\theta_{inductor} = \frac{T_{{inductor}\_ \max} - T_{{oil}\_ {avg}}}{Q_{inductor}}} & (2)\end{matrix}$

where Q_(inductor) is the heat loss in Watts.

Directly cooling the inductor assembly 14 using transmission fluidimproves the cooling capacity of the inductor by making the system moreenergy efficient (more fuel-efficient) and allows for a smaller andlighter inductor structure, which results in lower inductor cost. Thenew technique of splash ATF cooling of the inductor inside transmissionhousing offers a significant improvement in inductor (steady state)thermal capability and transient thermal performance.

FIG. 8 is a graph illustrating a comparison of the steady-state thermalresistance of the inductor assemblies of FIGS. 4 and 5, and isrepresented by numeral 400. Bar 410 represents the thermal resistanceCentigrade/Watts (C/W). Of an inductor assembly having a structure thatdoes not include a potting compound (e.g., the inductor assembly 14) andis mounted within a transmission chamber and directly cooled bytransmission fluid (as shown in FIG. 6). Bar 412 represents the thermalresistance (C/W) of an inductor assembly having a structure thatincludes a potting compound (e.g., the inductor assembly 100) and ismounted external to a transmission and is indirectly cooled by coolantthat flows through a cold plate (as shown in FIG. 4). Bar 414 representsthe thermal resistance (C/W) of the potted inductor assembly 100 whenmounted within a transmission chamber and directly cooled bytransmission fluid (not shown).

With a potted inductor (e.g., inductor assembly 100), the thermalresistance 412, 414 is approximately the same with both cooling methods,resulting in the same steady state thermal performance but bettertransient thermal performance (not shown). However, the impact ofdirectly cooling the inductor using transmission fluid is pronouncedwhen an un-potted inductor (e.g., inductor assembly 14) is used. Thedifference between the thermal resistance for un-potted inductor that isdirectly cooled 410 (0.18 C/W) and a potted inductor that is bothdirectly and indirectly cooled 414 (0.51 C/W) is approximately 65%.

With reference to FIG. 9, during operation of a PHEV in electric vehicle(EV) mode, it is common for an inductor assembly to experience highcurrent transients and heat load transients. Vehicle thermal managementsystems utilize high time constants to control inductor temperature sothat it does not exceed predetermined temperature limits. FIG. 9 is agraph illustrating a comparison of the thermal impedance of a pottedindirectly cooled inductor assembly and an un-potted directly cooledinductor assembly, and is represented by numeral 500. Such thermalimpedance values over time correspond to the transient performance ofthe inductor assembly. The thermal impedance of an un-potted directlycooled inductor assembly (e.g., inductor assembly 14 of FIG. 6) isrepresented by numeral 510. The thermal impedance of a potted indirectlycooled inductor assembly (e.g., inductor assembly 100 of FIG. 4) isrepresented by numeral 512. As illustrated in the graph 500, the timeconstant of curve 510 is approximately one third of curve 512.Additionally, the thermal mass of transmission casing and other elementspresent inside of the transmission chamber contribute to the effectivethermal mass of the inductor, which slows down the warming of theconductor coil. Thus, the steady-state and transient thermal performanceis significantly improved with direct cooling of an un-potted inductorwhere the coils and cores are fully exposed to the transmission fluid(as shown in FIG. 6).

FIG. 10 illustrates spray cooling of the inductor assembly 14 accordingto one or more embodiment. The transmission 12 includes nozzles 98 fordirectly spraying the transmission fluid 96 on components within thehousing 90, according to one or more embodiments. Such a “spray” regionis referenced by letter B and is located in an intermediate portion ofthe chamber 92.

The inductor assembly 14 may be mounted in a different orientation inregion B, as compared to that of region A, based on packagingconstraints and the flow of transmission fluid 96. For example, theinductor assembly 14 illustrated in FIG. 10 is mounted transversely ascompared to the planar mounting configuration shown in FIG. 6. Theinductor assembly 14 may also receive transmission fluid 96 thatsplashes off of proximate rotating components (e.g., the planetaryoutput gear 40) in region B. Other embodiments of the transmission 12contemplate multiple nozzles in region B, or additional nozzles that aremounted in other locations of the chamber 92 (e.g., the nozzle 98illustrated in phantom line and shown in region A).

FIG. 11 illustrates cooling of the inductor assembly 14 by immersion.The transmission fluid 96 accumulates within a lower portion of thechamber 92. Such an “immersion” region is referenced by letter C. Theinductor assembly 14 is mounted in a planar configuration within regionC and immersed in the transmission fluid 96 in the illustratedembodiment.

With reference to FIG. 12, the inductor assembly 14 is mounted within arear chamber 550 of the transmission housing 90, according to one ormore embodiments. The transmission 12 includes one or more passages 510that connect the rear chamber 550 to the front chamber for enabling theflow of the fluid 96 between the chambers. Like the front chamber of thetransmission 12 (shown in FIGS. 1, 6, and 10-12) the rear chamber 550includes transmission fluid 96 for cooling and lubricating rotatingcomponents. Such rotating components displace or splash the transmissionfluid 96 onto proximately mounted components. Additionally, thetransmission 12 may include one or more nozzles 98 within the rearchamber 550 for spraying transmission fluid 96 on components. Such a“splash/spray” region is referenced by letter “D”.

Referring to FIG. 13, an integrated inductor assembly having acylindrical core is illustrated in accordance with one or moreembodiments and is generally referenced by numeral 600. The integratedinductor assembly 600 includes a conductor 610 that is formed into acoil, a unitary (one-piece) core 612 and an insulator 614 that areintegrally formed with each other. Similar to the planar inductorassembly 14 of FIG. 5, the integrated inductor assembly 600 is anun-potted design that is configured to be mounted within regions A, B,or C of the transmission chamber 92 (FIG. 1) or within region D of therear chamber 550 (FIG. 12).

With reference to FIG. 14, a cylindrical inductor assembly having acylindrical core is illustrated in accordance with one or moreembodiments and is generally referenced by numeral 700. The cylindricalinductor assembly 700 includes a conductor 710 that is formed into acoil, a two piece core 712 and an insulator 714 that physicallyseparates the conductor 710 from the core 712. Similar to the planarinductor assembly 14 of FIG. 5, and the integrated inductor assembly 600of FIG. 13, the cylindrical inductor assembly 700 is an un-potted designthat is configured to be mounted within regions A, B, or C of thetransmission chamber 92 (FIG. 1) or within region D of the rear chamber550 (FIG. 12).

As such, the inductor assembly 14, 600, 700 provides advantages overexisting inductor assemblies 100 by facilitating direct cooling of theconductor and core. Such direct cooling may be used for cooling existinginductor assembly 100 designs or simplified (un-potted) inductorassembly 14, 600, 700 designs.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A vehicle comprising: a transmission including aninductor assembly and at least one gear adapted to, when rotating,transmit torque between an input and output of the transmission andsplash fluid onto the inductor assembly to cool the inductor assembly.2. The vehicle of claim 1 wherein the inductor assembly furthercomprises: an insulator; a coil wound around the insulator and havingexposed surface area portions; and a core formed in a generally planarshape and supported by the insulator.
 3. The vehicle of claim 2 whereinthe inductor assembly further comprises at least one switch mountedexternal to the transmission and in electrical communication with thecoil.
 4. The vehicle of claim 2 wherein the core comprises a pluralityof elements that are spaced apart from each other to define air gapsbetween adjacent elements.
 5. The vehicle of claim 4 wherein the corefurther comprises an insulative spacer disposed between adjacentelements to maintain the air gap.
 6. The vehicle of claim 2 wherein theinsulator supports the coil and the core without an additional housing.7. The vehicle of claim 2 wherein the insulator supports the coil andthe core without insulative material disposed on an outer portion of thecoil, such that the coil is exposed to direct contact with fluid withinthe transmission to cool the coil.
 8. The vehicle of claim 1 wherein thetransmission defines a chamber and wherein the inductor assembly ismounted within an upper region of the chamber and the fluid accumulatesin a lower region of the chamber; wherein the vehicle further comprisesa nozzle disposed in the upper region of the chamber and adapted todisplace the fluid toward the inductor assembly.
 9. The vehicle of claim1 wherein the transmission defines a chamber and the inductor assemblyis mounted within an intermediate region of the chamber between an upperregion and a lower region; wherein the vehicle further comprises anozzle disposed in the intermediate region, the nozzle being adapted todisplace the fluid toward the inductor assembly.
 10. The vehicle ofclaim 1 further comprising: an engine coupled to the transmission; anelectric machine coupled to the transmission; and a driveshaft extendingfrom the transmission; wherein the at least one gear further comprisesintermediate gears adapted to transfer torque between at least one ofthe engine and the electric machine to the driveshaft.
 11. Atransmission comprising: a housing; and a planar inductor assembly (i)including an insulative bobbin, a coil wound around the insulativebobbin and having exposed surface area portions, and a core supported bythe insulative bobbin and (ii) disposed within the housing such that atleast a portion of the exposed surface area portions is exposed to fluidwithin the housing to cool the coil.
 12. The transmission of claim 11wherein the transmission defines a chamber and the planar inductorassembly is mounted within a lower region of the chamber, and whereinthe fluid accumulates in the lower region such that the planar inductorassembly is immersed in the fluid.
 13. The transmission of claim 11wherein the transmission defines a chamber and the planar inductorassembly is mounted within an upper region of the chamber, and whereinthe fluid accumulates in a lower region of the chamber.
 14. Thetransmission of claim 13 further comprising a nozzle disposed in theupper region of the chamber and adapted to displace the fluid toward theplanar inductor assembly.
 15. The transmission of claim 11 wherein thetransmission defines a chamber and the planar inductor assembly ismounted within an intermediate region of the chamber between an upperregion and a lower region; wherein the transmission further comprises anozzle disposed in the intermediate region and adapted to displace thefluid toward the planar inductor assembly.
 16. The transmission of claim11 further comprising: at least one element rotatably coupled to thetransmission and disposed within a chamber defined by the transmission,the element being in contact with the fluid and adapted to displace aportion of the fluid onto the planar inductor assembly during rotation.17. A transmission comprising: a housing; an inductor assembly disposedwithin the housing; and at least one element adapted to, when rotating,transmit torque between an input and output of the transmission anddisplace cooling fluid onto the inductor assembly.
 18. The transmissionof claim 17 wherein the inductor assembly further comprises: a bobbin; acoil wound around the bobbin and having exposed surface area portions;and a core formed in a generally planar shape and supported by thebobbin.
 19. The transmission of claim 18 further comprising at least oneswitch mounted external to the transmission to communicate electricallywith the coil.
 20. The transmission of claim 18 wherein the corecomprises a plurality of elements with insulative spacers disposedbetween adjacent core elements to define air gaps.
 21. The transmissionof claim 18 wherein the core comprises a plurality of elements that arespaced apart from each other to define air gaps between adjacentelements.
 22. The transmission of claim 21 wherein the core furthercomprises at least one insulative spacer disposed between adjacentelements to maintain the air gap.
 23. The transmission of claim 18wherein the bobbin supports the coil and the core without an additionalhousing.
 24. The transmission of claim 18 wherein the bobbin supportsthe coil and the core without potting compound disposed on an outerportion of the coil.
 25. The transmission of claim 17 wherein thetransmission defines a chamber with an upper region and a lower regionand wherein the inductor assembly is mounted within the upper region ofthe chamber and the cooling fluid accumulates in a lower region of thechamber.
 26. The transmission of claim 25 further comprising a nozzledisposed in the upper region of the chamber to displace the coolingfluid toward the inductor assembly.
 27. The transmission of claim 17wherein the transmission defines a chamber and the inductor assembly ismounted within an intermediate region of the chamber between an upperregion and a lower region; wherein the transmission further comprises anozzle disposed in the intermediate region to displace the cooling fluidtoward the inductor assembly.
 28. The transmission of claim 17 whereinthe at least one element further comprises three intermediate gears, theintermediate gears being coaxially aligned and adapted to transfertorque between at least one of an engine and an electric machine to adriveshaft.
 29. The transmission of claim 17 wherein the at least oneelement further comprises a shaft.